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Fabrication line for drawn and punched components

Hydraulic drawing and punch press forms pressure vessel from coils


Pressure vessels for vehicles and compressors must meet demanding quality requirements. in order to fabricate these parts economically and at the required quality, a well-known vessel manufacturer was looking for new approaches to manufacture pressure vessels as drawn components directly from coils. In this case, the proposed press not only needed to demonstrate its cost efficiency for the planned production line, but also for other drawing and punching tasks that placed significant off-centre loads on the ram due to the part geometry. 


Selecting a manufacturer who was able to deliver a drawing press with 5000 kN from the group of well-known suppliers was relatively straightforward. Implementing the specification with respect to automating production proved to be more difficult. In this case, the field of contenders already thinned noticeably, and it was further reduced when the requirement for large off-centre loads needed to be met. After extensive research, the proposal forwarded by Dunkes from Kircheim/Teck was moved into the spotlight . The Swabian machinery builder compelled with its proposal, specifically with respect to technical considerations,  was furthermore in a position to assume the lead role for the planning effort, and to jointly implement the production line with external partners.

The production line forms or punches stainless steel sheetmetal in deep drawing grade with coil dimensions of 1050 x 5 mm and 700 x 6 mm into compressed air vessels. The sheetmetal is delivered as a coil at weights of up to 8 000 kg, and are brought to the decoiler with a hoisting device. After the steel is straightened in a 9 roller straightening machine, a servo controlled feed mechanism transports the coil with an accurately defined path into the workspace of the press. In order to integrate these preparatory activities into the automated process sequence, the coil plant is equipped with a programmable feed for the straightening head, an automatic coil transfer, an feed alignment aid for the coil, as well as an automatic coil thickness measurement unit.


The centrepiece of the production line is a hydraulic double column press with 5000 kN of press force from the Dunkes HDZ type series. In contrast to the standard configuration, the press frame was designed for a load of 5600 kN. This allows the user to temporarily also produce components that exceed the performance range of the standard press. The machine has an overall weight of 75 tonnes and sits on high-capacity vibration dampers that rest on four inward facing supports. This design detail reduces the overall height, while only immaterially increasing the standard table height. An important feature of these machines is the hydraulically controlled die cushion, which permits passive as well as active drawing processes. An 8-fold flat way of the ram with adjustable guides on each side is standard equipment and permits off-centre forces to be largely compensated. The parallel position of the RAM is ensured by a combination of a mechanical stroke limiter, coupled with four dampers and controlled by a special hydraulic system. The cutting force damper is designed for the max. press force. Performance degradations do not occur. The hydraulic ejector/ hold-down is installed in the centre of the ram. The high press weight results in a rigid frame with optimal cutting force damping characteristics; the noise profile during punching operations is significantly reduced.


The production line, which is controlled as a unit from the user programmable monitor control on the press, has been working in multi-shift operation since the fall of last year to the customer's full satisfaction. The pressure vessels with their various dimensions are fabricated in  single minute cycle times. A particularly noteworthy fact is that the plant was able to assume operations only a few days after delivery. The fast, disruption-free commissioning yet again confirmed the expertise of Dunkes as a manufacturer of hydraulic presses and as a lead engineering partner for automatic production lines. Since the press from the Dunkes HDZ type series was also able to compel with its extremely high rigidity, the guide characteristics of the ram for off-centre loads permitted the transfer of additional drawing and punching work, therefore offloading an older model press. The required flexibility improvement was therefore also attained.

Production line, consisting of loading rig, uncoiler, straightening machine, and hydraulic drawing and punching press, for punching and deep drawing pressure vessels.